Electric multi-phase machines are utilized in a wide variety of applications. As used herein, the term “multi-phase” refers to three or more phases, and can be used to refer to electric machines that have three or more phases.
For example, many hybrid/electric vehicles (HEVs) include an electric traction drive system that includes a three-phase permanent magnet alternating current (AC) electric machine that is driven by an inverter module. The inverter module is supplied with power from a direct current (DC) power source, such as a storage battery. Windings of the three-phase AC electric machine can be coupled to inverter sub-modules of the inverter module. Each inverter sub-module includes a pair of switches. A pulse width modulation (PWM) module receives voltage command signals and applies PWM waveforms to the voltage command signals to control pulse width modulation of the voltage command signals and generate switching vector signals that are provided to the inverter sub-modules of the inverter module. When the switching vector signals are applied, each pair of switches in each of the inverter sub-module switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric machine, which in turn drives a shaft of HEV's drivetrain.
Many modern AC machine drives use vector control to control the torque applied to the shaft (and thus the angular velocity or “speed”) of a rotor of the AC electric machine by controlling the current fed to the AC electric machine. In short, stator phase currents are measured and converted into a corresponding complex space vector that is then transformed to a coordinate system rotating with the rotor of the AC electric machine.
During a fault condition, it is desirable to deviate from normal operation and to apply either an open-circuit fault response or a short-circuit fault response at the inverter module to minimize the electric machine's torque response. Whether an open or short-circuit fault response is applied at the inverter module depends upon the machine's angular velocity (or “speed”). One approach for determining whether an open or short-circuit fault response is to be applied is disclosed in U.S. Pat. No. 7,279,862 B1 and Reissue Pat. RE 42,200, entitled “Fault Handling of Inverter Driven PM Motor Drives” assigned to the assignee of the present invention, their contents being incorporated by reference in their entirety herein.
In most systems, the instantaneous angular velocity of the machine's rotor can be determined based on the output of a position sensor or read directly from a speed sensor. In some situations, however, these sensors may themselves experience a fault, and therefore, the particular instantaneous angular velocity can not be easily determined (i.e., read from a angular velocity sensor or determined from the position sensor). Thus, when the speed/position sensor fails, the angular velocity of the machine is not available, and can not be used to make a decision regarding whether an open-circuit fault response or a short-circuit fault response should be applied at the inverter module to minimize torque response of the machine.
It would be desirable to provide improved methods and apparatus for determining whether an open-circuit fault response or a short-circuit fault response should be applied at an inverter module. It would be desirable if such methods and apparatus can function even when a speed and/or position sensor fails, and angular velocity of the machine is not available for making such determinations. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.